That is a pair of ridiculously open-ended and multi-faceted questions.

Any sort of spark of an idea can get world-building started. Some will go high-science and design full planets and solar systems within physical constraints, where others are more fantasy in their approach and just have a cool aesthetic they are going for. Of course, those are both over-simplifications.

Usually, though, worldbuilding begins with a premise. That premise might be something of a scientific bent (e.g. "What would a planet in a binary star system be like?"), or of a conceptual bent (e.g. "What if the world were a ring world?") or just a thought (e.g. my Mto, which has the premise of "What if the gods were real, and were playing Civilization with the world?").

Are you building a world for a story? Are you building a world for the fun of it? You're potentially going to look at radically different things.

Once you have a premise, you start filling in details as seems appropriate. Ask questions (or look at lists of questions, or engage in e.g. the Conpeople Opinions thread that I've sadly not participated in for a long while) and think through what the answers might be, as relevant to your goals.

I don't know what other sort of answer to give without even knowing to what end the worldbuilding is taking place, or what the actual goal is.

For me, the goal is that I want to create a reasonably realistic and thought-through world in which to set a series of stories/novels. That's my driving force, though it hasn't stopped me from delving into the underlying physical values of the world's solar system and therefore calendar et cetera. But, your goals may differ, and so your methods and aims may differ.

Really, this is all to say: that question doesn't give us enough information to answer it.

Mgmg. Those are two very deep questions indeed! I think as you can see already from our replies that these questions can be seen as quite, well, useless if you take my meaning. It's like asking "How do I start my day?" and "What I do from there?" There are at least a thousand and one ways to answer those questions and ten thousand and one directions to go from there.

As is often the case, I'm going to go in a different direction from all the other perfectly awesome advice you've been given.

I'm pretty strongly of the opinion that the best way to engage in an art like this is to just do it. Sort of push you into the metaphorically deep end of the pool and let you sort it out on your own. Then, once you figure it out, start learning some of the theory. My fear is that if you read books & websites on how to do it too soon, you'll just end up following that writer's recipe. Keep following the recipes and you end up with batch after batch of the same cookies. All of those books and how-to blogs I think they tend to lead us, wittingly or unwittingly, down the path that the writer has chosen to take rather than the path that's best for you. At best, they can offer you some tips and theoretical knowledge, but no one, not me, not a book, can actually tell you how you must go about doing this!

How to start? Maybe try just sitting back, letting your mind wander... Push through the mists that separate worlds and step out into a different one... Begin to explore! Rather than trying to make a world, just look around and find out what's already there!

Where to go from there? Well, anywhere! You aren't bound by time and place. Just go and explore. If you see a grand city, go back and observe its founding and what was there before. Visit with people, learn their ways and their stories.

Your own deepest of hearts will lead you to a world you need to be in. After that, it's just a matter of absorbing the experience and then coming back and telling us about it!

If we stuff the whole chicken back into the egg, will all our problems go away? --- Wandalf of Angera

Usually, though, worldbuilding begins with a premise. That premise might be something of a scientific bent (e.g. "What would a planet in a binary star system be like?"), or of a conceptual bent (e.g. "What if the world were a ring world?") or just a thought (e.g. my Mto, which has the premise of "What if the gods were real, and were playing Civilization with the world?").

I'm not sure that's true, at all. Fantasy worlds, in particularly, are often not driven by any specific premise. My own just grew out of a place to set various stories, and later languages. Different parts of it, of course, could be described as having underlying premises, but the whole, I think, lacks any clear conceptual driving force.

Contrariwise, my SF setting is indeed driven almost entirely by its premises.

Fantasy worlds, in particularly, are often not driven by any specific premise.

Many of them are pretty loose premises, such as "what if magic were real?"

But yes, you can have a world that's just "let's make shit up", and seeing where it goes from there. I'd still challenge the idea that there aren't any underlying world-spanning premises in there, even if it's just "what if not Earth?"

Of course, now I'm bordering on the so-global-it's-inane side of the spectrum, so...

With a lot of "worldbuilding", there's a lot of "your mileage may vary". Hence going back to the problem with the original question. ‍♀️

Fantasy worlds, in particularly, are often not driven by any specific premise.

Many of them are pretty loose premises, such as "what if magic were real?"

But yes, you can have a world that's just "let's make shit up", and seeing where it goes from there. I'd still challenge the idea that there aren't any underlying world-spanning premises in there, even if it's just "what if not Earth?"

Of course, now I'm bordering on the so-global-it's-inane side of the spectrum, so...

I think my point would be that just because you can identify a fact about something (like "magic is real here" or "this is not Earth", that doesn't mean it was the premise upon which it is predicated. I mean, you could say Fatherland's premise was "what if tall building in Berlin?" on that basis - but I don't think that's really what the author had in mind.

[And with respect, I don't think that what I'm doing, even if it does differ from what you'd recommend, is just "making shit up"; personally, I think I put as much thought into it as anyone else. And indeed, I think that "premise"-based conworlds can often feel rather one-dimensional and superficial, if they're not able to move away from the premise sufficiently.]

With a lot of "worldbuilding", there's a lot of "your mileage may vary". Hence going back to the problem with the original question. ‍♀️

...I don't disagree with the first two sentences there. But, and I know I risk coming across as some unwoke troglodyte here, but I've honestly been racking my brains - what is the "woman woman" bit meant to indicate in this context? I can't work out what the implication is meant to be.

I think my point would be that just because you can identify a fact about something (like "magic is real here" or "this is not Earth", that doesn't mean it was the premise upon which it is predicated. I mean, you could say Fatherland's premise was "what if tall building in Berlin?" on that basis - but I don't think that's really what the author had in mind.

I think I'd agree with that. A lot predicates on the semantic meaning of "premise", and that's an argument I'd rather not have.

I don't think that what I'm doing, even if it does differ from what you'd recommend, is just "making shit up"; personally, I think I put as much thought into it as anyone else.

With all due respect, I don't think "making shit up" and "putting thought into it" are contradictory. After all, we're all just inventing fictions :)

what is the "woman woman" bit meant to indicate in this context?

That's the shrug emoji apparently being mangled by the forum software being unable to understand modern Unicode properly.

This would be a great time for our OP to pop back in and give this thread a purpose before it becomes something else...

Yes, I would also say that an important part of worldbuilding (and any sort of creative endeavor) is engaging with a community of people doing the same activity (or at least, who consume the things you produce) and getting feedback, and being part of the conversation. As iron sharpens iron, so we sharpen each other.

I've recently started working on worldbuilding that I am hoping to leverage into a writing project. So I'll answer form my perspective.

I started with a question I thought would be fun to answer. "How can you have a world that seems wild and chaotic, while have a solid consistent logic underneath?" This stems from my personal preference to avoid the feel that things are being made up as you go along. I want everything to make sense when you understand all the pieces. I just don't want to show all the pieces to the people in the world, or the reader.

So once I had that question everything flowed from there. I can up with what I thought was a plausible way to handle what I wanted, and then built a back story and world to match that answer.

I've posted an intro to this world building in another thread if you're interested.